ISLAMABAD/DERA ISMAIL KHAN, Pakistan — The chief of the Pakistani Taliban was killed by a U.S. drone strike on Friday, security sources and a senior Taliban commander said, in the latest in a series of setbacks for the insurgent group.

.Hakimullah Mehsud was one of Pakistan's most-wanted men, with a $5 million U.S. bounty on his head. He led an insurgency from a secret hideout in North Waziristan, the Taliban's mountainous stronghold on the Afghan border..."We confirm with great sorrow that our esteemed leader was martyred in a drone attack," a senior Taliban commander told Reuters.

In Washington, two U.S. officials confirmed Mehsud's death in a CIA drone strike. They spoke on condition of anonymity...The Pakistani Taliban, a fragmented group aligned with its Afghan namesakes, has staged attacks against armed forces and civilians in its fight to topple Pakistan's government.

The death will likely scuttle the immediate prospect of peace talks between the Taliban and the new government of Prime Minister Nawaz Sharif, who won a landslide election victory in May by promising to bring peace to Pakistan...Mehsud's funeral will be held today in Miranshah, the Taliban commander said — an event likely to stir tensions further in the volatile region.

The nuclear-armed nation of 180 million people has been plagued by militant violence, including the homegrown Taliban insurgency that has cost tens of thousands of lives...The Taliban had already been weakened by a series of recent counterattacks. In May, a U.S. drone strike killed Mehsud's second-in-command, and one of his most trusted lieutenants was captured in Afghanistan last month...The government never clarified which factions of the Taliban it was willing to talk to or whether it would comply with the Taliban's demands to release its prisoners and withdraw the army from Taliban strongholds in Pakistan's tribal areas.

Pakistan recently informed the United States and Britain that peace talks with the Pakistani Taliban were imminent, said Bruce Riedel, a former CIA and White House official with extensive experience in the region.

"So the drone strike is very awkward and difficult for Sharif. Conspiracy theories in Pakistan will assume he agrees to the strike even as he proposed peace talks with Mehsud," Riedel said via email. "Another setback for U.S.-Pakistan relations ironically."..The Pakistani Taliban acts as an umbrella for various jihadist groups operating in Pakistan's lawless tribal belt, which are separate, but allied to the Afghan Taliban.

On Friday, several intelligence, army and Taliban sources across Pakistan said Mehsud, believed to be in his mid-30s, had been killed in the drone strike in North Waziristan. Four security officials confirmed his death to Reuters. His bodyguard and driver were also killed, they said...The drones fired four missiles at a compound, sources said.

Mehsud had been attending a gathering of 25 Taliban leaders to discuss the government's offer of talks, they said...